Effect of centrifugal rotational speed on wedge castability of titanium

This study examined the effects of the speed and force in centrifugal casting on the wedge castability of Ti–5 mass%Cu (Ti–5Cu) alloy and commercially pure titanium (CP-Ti). The Ti–5Cu alloy was prepared by argon-arc melting. Whole wedge-shaped acrylic patterns were prepared with either 15° or 30° angles and invested with a MgO-based material. The wedge specimens were cast using a centrifugal casting machine at rotational speeds of 600, 1000, 1250, 1500 and 3000 rpm. Mold filling, an index for a measure of castability, was determined as the missing length between the edge of the cast wedge and the theoretical acute tip of the triangle. CP-Ti was used as a control. An analytical model was developed to relate the mold-filling index to the surface energy and rotational speed. The experimental results indicate that the means of the mold-filling index of the 30° wedge angle were lower than those of the 15° wedge angle when compared for each corresponding metal and rotational speed. In each angle for CP-Ti, the means tended to reduce with increase in the rotational speed. The mold-filling index of 5% Cu titanium was found to be similar to that of CP-Ti, even for 15° wedge when the rotational speed was higher than 1250 rpm. The results suggest that dental prosthesis, which has narrow cross sections containing very narrow regions (for example, clasps of a denture), can be cast successfully by utilizing high rotational speed during centrifugal casting. The complex dependence of mold-filling index on wedge angle and rotational speed is explained on the basis of the analytical model and the dependence of the apparent surface energy on rotation speed.